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The DECRYPT Project
Decryption of Secret Historical Manuscripts
  • Collection
  • Transcription
  • Decipherment
Go to the ciphers
in the DECODE database

NEWS: To learn more about the decipherment of Mary Stuart’s lost letters go to our Publications!

About Us

Cracking ciphers in a cross-disciplinary team

Thousands of enciphered historical manuscripts are buried in libraries and archives. Examples of such material are diplomatic correspondence and intelligence reports, private letters and diaries as well as manuscripts related to secret societies. The bulk of these historical manuscripts will remain undeciphered unless we can automate the processes involved in decoding them. Our aim is to develop resources and computer-aided tools for decoding of historical source material by using AI and cross-disciplinary research involving computational linguistics, computer vision, cryptology, history, linguistics and philology.

Within the DECRYPT project, we release resources and tools with open access to facilitate research in historical cryptology, allowing collection, analysis and decipherment of historical ciphertexts. Resources are collections of encrypted sources, and historical texts with language models. The tools facilitate the processing of the encrypted sources from transcription to decipherment. We list our resources and tools below, which are described in our scientific publications.

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Resources and Tools

The DECODE database contains a collection of digitized images of ciphertexts and encryption keys along with metadata information about their provenance, location, transcription, and possible cryptanalysis or commentary. The database enables search and all records in the database are open to the public. HistCorp is a collection of historical corpora and other useful resources and tools for researchers working with historical text. 

We provide tools for transcription and decipherment of historical ciphers using advanced machine learning algorithms. Historical cipher images can be transcribed, i.e. transformed into a computer readable text format with the help of the TranscriptTool. The transcribed ciphertext can be corrected and used as input to CrypTool which assists you in breaking a wide range of historical ciphertexts.  

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The DECRYPT Portal

PI

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Beáta
Megyesi

Project leader

Stockholm University

Sweden

Core Team

Participants

Further contributors

The DECRYPT Portal

Our resources and tools are open source and free

We provide a collection of encrypted historical sources, and tools for the automatic analysis and decryption using AI.

Resources
  • DECODE DATABASE

    a collection of thousands of historical ciphertexts and keys

  • HISTCORP

    a collection of historical texts and language models for 16 European languages

Transcription of Ciphers
  • CrypTool Transcriber and Solver (CTTS)

    a desktop tool for manual transcription

  • TranscriptTool

    a web-based tool for semi-automatic transcription using AI

Cryptanalysis
  • CrypTool 2 (CT2)

    a desktop tool for breaking historical and modern ciphers

  • CrypTool-Online (CTO)

    an online tool for breaking (simpler) historical ciphers

Terms of use

The source code of the platform and tools are being released as open source under the Apache license v.2.0 with the exception of the DECODE database with its special terms and conditions.

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DECRYPT Publications

2025

  • Bruton, M. and Megyesi, B. (2025) From Statistics to Neural Networks: Enhancing Ciphertext-Plaintext Alignment in Historical Substitution Ciphers for Automatic Key Extraction. In Proceedings of the 8th International Conference on Historical Cryptology (HistoCrypt 2025).
  • Palma, C. and Megyesi, B. (2025) DECODE2LOD: Connecting the DECODE Database with the Linked Open Data Cloud. In Proceedings of the 8th International Conference on Historical Cryptology (HistoCrypt 2025).

2024

2023

2022

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2020

2019

PhD Theses

Bachelor's and Master's Theses

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